1. Field of the Invention
The invention relates generally to the field of photography, and particularly to an electromagnetically driven actuator that moves one or more camera shutter blades.
2. Description of the Prior Art
Leaf type or blade type mechanical shutters have been used to regulate the amount of light that is going to reach the imaging areas of a filmstrip contained within a camera. Typically, the leaf type of shutter is an array of metal "blades" that are pivoted so that they all swing towards or away from the lens aperture of the camera. When the shutter is closed, all the blades are overlapping in the center of the lens aperture and no light reaches the filmstrip. When the shutter is open, the blades pivot away from the center of the aperture, so that light may pass through the aperture and expose the filmstrip. Sometimes an array of metal blades are not used, and the leaf type mechanical shutters may have one or more blades, each of which may have a different diameter opening. When a picture is taken the blade or blades swing away from the center of the lens aperture so that light may pass through the aperture, through the blade or blade openings to expose the filmstrip. If a picture is not being taken, the shutter will be closed. Hence, one blade may block the opening of the other blade, or both blades openings may not be in optical alignment with the aperture. The power to open and close the leaf type mechanical shutters is provided by a spring or springs that are under tension, and the timing is controlled by a watch-type gear train.
Electromagnetic shutters have been developed to reduce the amount of energy or power that is required to open and close leaf type mechanical shutters. Electromagnetic shutters are faster than mechanical shutters from 4 mm diameter to 20 mm diameter aperture openings and electromagnetic shutters may be controlled with greater accuracy than mechanical shutters. The manufacturing cost of an electromagnetic shutter is less than the manufacturing cost of mechanical shutters.
The prior art utilized solenoids with linkages that are coupled to the shutter blades to open and close electromagnetic powered shutters. Some of the disadvantages of prior art solenoids are: the solenoids used a large amount of current, i.e. approximately 2 amps; the solenoid had no intermediate positions, i.e., the solenoid and the lens aperture was either open or closed; and the solenoids were slow due to inertia required to move the large mass of the solenoids plunger.